1. Field of the Invention
The present invention relates to a method for verifying, or checking the plausibility of, a rotational direction of a rotating body, e.g., a vehicle wheel or of a shaft.
2. Description of the Related Art
The utilization of acceleration sensors is known for ascertaining the rotational direction and/or rotational speed of rotating or turning systems. In particular, wheel sensor modules which detect different measured variables are utilized in vehicle wheels, for example the tire air pressure, a temperature and the accelerations themselves, and communicate these measured variables or part of these measured variables via a transmitting device to a receiver on the vehicle body. In some cases it is provided that the wheel sensor modules themselves do not receive any data with locating information, and also that no data are sent by the vehicle in such a way that their position on the vehicle is recognizable from the receiving characteristics of the electronics. The position on the vehicle is also not known by programming the wheel electronics. Hence it is provided in such systems that the wheel sensor module itself ascertains the rotational direction, and that it may be established from the rotational direction whether the vehicle wheel is located on the left or right side of the vehicle.
It is known from published German patent application document DE 10 2007 046 308 A1 to place acceleration sensors on the vehicle in a tangential direction with a 90° phase shift, so that the acceleration sensors each convey the product of the gravitational acceleration and the sine function or cosine function of an angle which determines the rotational position of the vehicle wheel. It is thus possible to deduce the rotational direction depending on whether the phase shift during the rotational motion is positive or negative; a vernier method is employed to evaluate the ascertained phase differences. Moreover, in addition to the rotational direction, the rotational speed or rotational frequency of the vehicle wheel is also ascertained.
Such direct determination of the rotational direction from ascertained phase differences and assignment of the phase differences to a sine and cosine function or two phase-shifted sine functions is not always clear, however, not even after deducting the offsets of the signals. This is the case in particular if the measuring signals deviate from a pure sine or cosine, for example due to a rough subgrade or a change in the vehicle velocity. It has been found that with multiple measurements and corresponding evaluations, by assigning the phase difference to a rotational direction, sometimes contradictory results may arise in ascertaining the rotational direction.
Placing two sensor devices on the wheel with a 90° phase shift makes it possible to obtain pure tangential acceleration measurements without a contribution of the centrifugal acceleration; but this is very complicated and costly. When acceleration sensors with other detection directions are used, a radial acceleration component must be taken into account, which is determined in particular by the centrifugal force when the vehicle wheel is turning. The centrifugal portion of the acceleration values can be calculated by deducting a mean value or determining a linear or polynomial fit from the source data.
Published German document DE 603 08 213 T2 shows a device for determining the position of a vehicle wheel, which is usable in particular with a tire pressure sensor module. The device has two acceleration sensors, whose detection directions each have a component in the vertical plane with an angular offset of 0° and 180°. With this system too, the phase shift between the measured acceleration signals is ascertained and from it the rotational direction of the vehicle wheel is determined, from which the wheel can be located on the vehicle.
Published international patent application document WO 2005/069993 A2 describes a tire sensor module for vehicle wheels that has a pair of motion sensors from whose measuring signals a position of the vehicle tire is ascertained, wireless signals being emitted to a receiving device on the vehicle.